Turning Units – static

If you have access to a decent amount of green waste and if you have the space in your garden you may decide that you want to expand into a 2 or 3-bin-system and try your hand at hot-composting. Bins such as these are known also as static-turning-units. Two units will allow you to have one batch of ingredients composting while you build up stocks for your next batch and if you expand into three, you will be able to manage your pile really efficiently with the option of having a container where your compost can mature once it has cooled down and bacterial and animal activity has ceased.

Managing hot-composting in multiple static-turning-units takes some degree of organisation and physical fitness, but there is no doubt that many gardeners look upon this as the best method of all. There seem to be as many ways of doing it as there are gardeners, however. To each his own, I guess.

David, on his allotment, runs a system of static-turning-units. He does not do much turning, so does not achieve very high temperatures. Hot-composting is not a priority for him. He reserves bin 1 for new stuff. When it is full and activity has under-way, its contents are turned into bin 2. When he is satisfied that the contents of bin 2 are well processed, he turns them into bin 3 for maturing and to stand until it he is ready to use it. Other gardeners argue that one space should be left free so that there is always an area for turning into. Others believe that once activity has ceased you should sieve the contents in order to separate any bits not fully decayed and use the fine stuff immediately. The partly-decomposed material should then be returned and mixed with the compost which is still active. Others just fill the three bins altogether and let the compost rot down with minimum interference. No doubt each theory has its own proponents who seriously believe their way is best. You will find your own way as your experience grows.

4-bin turning units from breeze-blocks

The University of California lists the procedures they recommend for managing static-turning-units with 3 compartments and they are quite precise. They suggest that raw materials be added to an end bin with the addition of about one cup of fertiliser containing nitrogen as a starter if ‘greens’ are in short supply. They also recommend the addition of a thin layer of soil to introduce the micro-organisms needed to carry out the composting. This is a once-only requirement. Theyadvise that you dampen your materials as usual. After a few days, start checking temperatures – you are aiming for the centre to reach around 140 – 150o F. Once this has been achieved, you turn your compost into the next bin making sure to bring the goodies on the outside into the middle and those in the middle to the outside. When this pile reaches around the 140-150o F. mark,you turn it back into the original bin and repeat the process.

Steaming away nicely!

Eventually, you will need to turn your pile less frequently. The micro-organisms will complete their task, the temperature will drop and hot-composting will cease. At this point, you turn your compost once more into the third bin and leave it there until you need it. (this is when you can sieve it to remove any material not quite ready).

Now – it is time to start hot-composting again with a fresh load of ingredients.

To sum up, (quoting the University of California document) “once set up, the three-bin composting system will consist of one bin with yard waste being composted; one bin empty, to or from which the compost is turned; and one bin containing finished, or nearly finished, compost.”

Be aware that the speed of decomposition is increased the more you turn your materials as this introduces added oxygen to your pile. However, your management of the system and the types of materials you are composting has a major part to play in the rate at which your compost is made.

As far as building a series of static-turning-units is concerned, there are many ways – pallets, breeze blocks, old deck planks or wire enclosures. If using timber, be careful that it has not been treated with preservatives as these will pollute your compost. You can purchase commercially manufactured static- turning-units which saves a great deal of pressure if you are not a handy type. One of the best of these is known as the New Zealand box (it was invented there) and it is special in that the front is comprised of a series of slats that slide up and off, allowing access to your compost and making turning a lot easier.